Despite efforts to become a paperless society and regardless of the prevalence of email communications, facsimile (or fax) transmission of printed materials (e.g., text, photographs, or the like) remains vital, particularly for business users. One reason for the continued popularity of faxes is that, unlike email attachments or digital signatures, the signature on a fax document is legally binding. Moreover, fax documents retain the format of the original source document and are virtually uneditable.
A traditional analog fax generally involves the transmission of scanned-in printed material (text or images), usually to a telephone number associated with a printer or other output device via a public switched telephone network (PSTN), as specified, for example, in the International Telecommunication Union (ITU) T.30 standard (see, e.g., ITU-T Recommendation T.30, Series T: Terminals for Telematic Services, Procedures for Document Facsimile Transmission in the General Switched Telephone Network, September 2005, the disclosure of which is incorporated by reference herein in its entirety for all purposes). An original source document is scanned-in by a fax machine, which treats the contents as a single fixed graphic image, converting it to a bitmap. Once in this digital form, the information is transmitted as electrical signals through the telephone system. The receiving fax machine reconverts the coded image and prints a paper copy of the document.
As the transmission of voice over the internet, using voice over internet protocol (VoIP) technology, permeates private and public organizations, such organizations find it desirable to leverage the value and convenience of their single, distributed IP communications network. Since fax transmissions generally utilize the same facilities as voice communications, it is becoming increasingly popular to implement fax transmissions using facsimile over internet protocol (FoIP) as specified, for example, in the ITU T.38 standard (see, e.g., ITU-T Recommendation T.38, Series T: Terminals for Telematic Services, Facsimile—Group 3 Protocols, Procedures for Real-time Group 3 Facsimile Communication Over IP Networks, April 2007, the disclosure of which is incorporated by reference herein in its entirety for all purposes).
One known method of sending fax images and modem data over a packet network is by way of voice band data (VBD), as specified in ITU V.152 standard (see, e.g., Recommendation ITU-T V.152, Series V: Data Communication Over The Telephone Network, Interworking with other networks, Procedures for supporting voice-band data over IP networks, September 2007, the disclosure of which is incorporated by reference herein in its entirety for all purposes). VBD is widely used in media gateway systems and analog telephone adapters (ATAs) because it is simple and easy to implement, and it transmits fax and modem data the same way as it does for voice traffic. However, a major disadvantage of VBD in gateway and ATA systems is its inability to handle packet losses and burst jitters (e.g., variable delay) that are common in an IP network. For this reason, T.38 was adopted by ITU, and supported by many commercial gateway and ATA products. However, the T.38 standard does not compensate for transmission problems between gateways/ATAs and end devices, such as traditional facsimile machines. A traditional VBD session for fax transmission over IP networks needs gateways or ATAs to convert analog signals (from/to a traditional fax machine) to digital packets, as shown in a prior art system 100 in FIG. 1. FIG. 1 shows traditional fax machines 105-1 to 105-4 connected to IP network 130 by way of PSTNs 110-1, 110-2 and VBD-enabled gateways 115-1, 115-2 and by way of VBD-enabled ATAs 120-1, 120-2. Only with the help of VBD capable gateways and ATAs can the fax machines in FIG. 1 engage in VBD-based VoIP fax sessions.